Hydraulic pumping apparatus and method of operation

摘要

A hydraulically actuated pumping apparatus including a piston-driven, plunger-type injection pump in combination with a three-way normally closed pilot-operated relay valve, and a variable restrictor adjustable during operation of the pumping apparatus for controlling the flow of a pilot fluid to the relay valve. Pilot fluid is vented from the relay valve through passageways in the plunger of the injection pump at the completion of each pumping stroke.